1. Field of the Invention
This invention relates to a power screwdriver, and more particularly, to a transmission mechanism, such as clutches or ball bearings, built into the screwdriver for disconnecting rotating force from a motor to a driver bit.
2. Description of Related Art
A conventional power screwdriver is commonly used for driving a fastener, such as a screw, into various work surfaces. Such power screwdrivers do not provide a means for automatically stopping the rotation of a spindle which holds a driver bit. To use such a power screwdriver, an operator must know when to stop applying power to the motor with a trigger switch to stop the rotation of the motor. However, when a screw is driven into a delicate material, such as dry walls, a delay in disconnecting power to the motor may damage the work surface or may result in an excessive penetration of the screw into the work surface.
Some power screwdriver is equipped with a clutch mechanism to either transmit or disconnect the rotation force from the driver motor to the spindle. The clutch mechanism includes a fixed clutch connected to the driver motor and a movable clutch which engages or disengages the fixed clutch in response to the pressure applied to a housing surrounding the driver bit when the housing is pressed against the work surface. During the disengaging operation, the separation of the clutches is usually abrupt and causes early wear of gear teeth. Similarly, when two clutches reengage each other, the gears or teeth of two clutches grind against each other to foster early wear.